Lattice mast structures of the above-designated type are open steel framework constructions with angle profiles or round profiles on bridges, in the form of pylons or power line masts. Such lattice mast structures have the advantage that they are particularly lightweight and can be built up easily. Particularly if the lattice mast structure consists of angle profiles, the individual profile struts can be connected to one another relatively easily, for example by riveting, welding or bolting.
Lattice mast structures are predominantly used as lattice masts for receiving overhead electricity transmission lines. Lattice masts are usually built up from a series of structural elements arranged above one another, with each stage forming a framework structure which has three or more trapezoidal framework panels which each consist of supports which are braced to one another. The supports are designed as angle profiles, and the struts connecting them in the form of cross-struts or diagonal struts can also be formed in part as angle profiles, and in part also as plate profiles.
The design of such framework structures is generally subordinated to the requirements for the bearing load and for the wind load acting on the construction. Furthermore, the forces from intrinsic weight, tensioning, ice and temperature have to be taken into account in the design.
The dimensioning of the structural elements forming the framework structure is dependent, on the one hand, on the free buckling length of the individual elements and on the tensile or compressive stress prevailing in the latter and, on the other hand, on the interaction of longitudinal forces and lateral forces which are introduced into the construction, for example, by wind loads.
In order to stabilize lattice constructions or framework structures of the above-described type, numerous bracing systems are known which are optimized with respect to the arrangement of the framework struts and with regard to the total weight of the lattice structure. Such a system is described, for example, in GB 675,859 A.
The optimal design of the structure for the expected wind load and bearing load relative to the optimal weight generally presents relatively few problems in the erection of new lattice masts or lattice mast structures.
In the case of existing lattice masts for overhead electricity transmission lines, for example, it may be necessary from time to time to repair and/or replace parts of the structure. In some circumstances, this requires new stability checks. Existing installations do not meet increased stability requirements in some circumstances, in particular also owing to increased load requirements or owing to a structural weakness which is to be expected after standing for a relatively long period of time.
It is sometimes necessary for lattice masts to receive additional lines on their mast cross-arms because, for example, a greater electrical power has to be provided in an electrical power network.
In such cases, an upgrading of the existing lattice masts is required, in particular if the free buckling length of the steel profiles is not designed for an increased bearing load or the cross section as such does not have sufficient bearing capacity.